SA Water treats water supplies for drinking water to protect public health. As a result, residual levels of chemical substances used in the process may be unsuitable for aquariums or ponds with aquatic fauna.
The two most common methods of disinfection are:
- chlorination (using chlorine)
- chloramination (using chloramines)
We use chloramination in some of our systems as it lasts longer when compared to chlorine.
A combination of ammonia and chlorine forms chloramines. These are toxic to fish at levels as low as 0.1 milligrams per litre. As a result, you should remove them from tap water before use in fish aquariums or ponds. Some free ammonia may also be present in chloraminated water. Ammonia can be toxic to fish, but may be present in fish aquariums as a natural waste product.
Exposure to sunlight can remove chlorine within several hours. For chloramines, it may take weeks to completely break down. Chloramines are generally removed by a de‐chlorinating agent (usually sodium thiosulphate). This can be found in aquarium water conditioning agents, or by filtration through high-quality granular activated carbon. If using chloramines, you can ensure particular care through the following:
- When using a commercial aquarium water conditioning agent, use two to three times the recommended dosage. This will help remove the high levels of chloramines in treated water.
- You may prefer to use pure sodium thiosulphate. Most de‐chlorinating agents contain other additives for slime protection and water ageing. These may be harmful in higher dosages. When using pure sodium thiosulphate, the recommended dosage is 10 milligrams for every 1 milligram of chloramines (or chlorine) per litre. For example, you will need 30 milligrams for 3 milligrams per litre of chloramine.
- De‐chlorinating agents remove chlorine, but will leave ammonia. You should either control or remove the ammonia, as detailed further below.
Granular activated carbon works well when removing chloramines. Its useful life depends on the size and type of carbon used, and conditions such as pH, flow rate and contact time. Careful monitoring using a test kit is necessary to ensure satisfactory results. The use of the carbon may be particularly suitable for outdoor ponds.
Removal and control of ammonia
Some ammonia will be present in chloraminated tap water. The use of carbon will produce ammonia, as will de-chlorinating agents when removing chloramines. You can remove or control ammonia using the following methods:
- Nitrifying bacteria: In a pH neutral tank, nitrifying bacteria removes the ammonia. This can be produced from fish waste and from the breakdown of protein in uneaten fish food. These bacteria grow on solid surfaces such as gravel, sand or filter material. This method is not suitable for new aquariums as it could take up to six weeks for the bacteria to function.
- pH control: Keeping the pH to 7.5 or lower can control the toxic effects of ammonia. It is important to keep checking levels. pH test kits and correction chemicals are available from aquarium retailers. This method is unsuitable for certain aquarium fish, such as marine species that need a high pH.
- Ammonia removal resins: Placing these inside a box or canister filters in a tank can reduce ammonia levels. Again, this will need two to three times the recommended dosage. The resins will remove high levels of ammonia. This method is not suitable for salt water.
Important things to consider
- You should neutralise chloraminated tap water before it's used in fish aquariums.
- It is good practice to make smaller, more frequent, water changes. This minimises the risks involved when using tap water containing chloramines.
- Recommended dosages may not be enough when removing chloramines and ammonia from South Australian drinking water.
- Some treatments are not effective, such as boiling the water and letting it stand outside for a day or two. This also includes using chemicals that only remove chlorine, or using a reverse‐osmosis filter.
Where can I get more information?
Local pet shops or aquarium retailers will be able to provide you with further information. You can also contact the SA Water Customer Service Centre on 1300 650 950 if you need help. We've prepared this page to give you a broad outline of disinfecting tap water for ponds and aquariums. We still recommend you look for specific advice based on your needs. Remember to check water conservation measures for fountains, ponds and water features in your local area.